The present invention relates to a securement device for securing a steering spindle bearing unit on a bracket unit of an adjustable steering column for a motor vehicle. The securement device comprises at least one clamping device and at least one locking element, activatable by the clamping device, as well as at least one counterlocking element. The locking element and the counterlocking element, in a closed position of the clamping device, are disposed in an engagement position, and the securement device comprises at least one resilient reset element for resetting the locking element in an open position of the clamping device.
In adjustable steering columns for motor vehicles, securement devices are employed in order to secure or lock the adjustable steering column in the set position for normal operation of the motor vehicle. When the securement device or its clamping device are in an open state, the steering wheel attached on the adjustable steering column can be adjusted by the driver of the motor vehicle into the desired position in the height and/or length direction. In the prior art, such securement devices are also referred to as clamping systems. There are securement devices that are based on the engagement of locking and counterlocking element under form closure. However, there are also securement devices in which by means of a clamping locking element and counterlocking element in the closed position of the clamping device are exclusively in operational connection under friction closure. Friction closure is disclosed in prior art for example in EP 0 802 104 A1.
The problem encountered in the case of clamping under friction closure is attaining sufficient fixedness and resistance of the connection against a dislocation of the steering column during the operation of the motor vehicle. In many cases, in particular high fixedness of the connection is to be ensured even in the event of a crash. However, simultaneously the capability of simple adjustments is also to be given in the open position of the clamping device. In general, it is herein preferred for the adjustability of the steering column in the height and/or length direction to be an infinite one.
EP 0 802 104 A1 proposes the use of several frictional faces in order to increase the frictional force correspondingly. DE 196 43 203 A1 shows an example of the connection under form closure by means of teeth engagement known in the prior art. However, this technology also entails various problems. On the one hand, not every adjustment position can be set and, on the other hand, there is always the risk that when closing the securement device the tips of the toothings corresponding to one another impact one another and, accordingly, no secure engagement takes place. A further disadvantage of such form-closure solutions involving toothing engagement is that in the open position of the clamping device a free-moving friction closure clamping of the steering column must be achieved using special means such that the column does not rattle and is smoothly adjustable.
A generic securement device is shown in DE 10 2007 003 091 B3. In this implementation according to the prior art, the form-closure engagement of locking element and counterlocking element is again achieved by means of toothing when the clamping device is in the closed position. In the open position of the clamping device, the locking element is lifted out of the toothing of the counterlocking element by spring arm-like resilient reset elements. This is intended to ensure that relatively high holding forces can be provided. On the other hand, for the case of very high forces occurring, for example in the event of a motor vehicle crash, a form-closure connection between locking and counterlocking element is to be effected via the edge-side toothing. The implementation shown in DE 10 2007 003 091 B3 entails the above listed disadvantages of engagement by toothing. Especially with frequent adjustments of the steering column, the toothings can become only half engaged. A disadvantage of this solution according to the prior art between locking and counterlocking element accordingly consists in damage to the edge-side teeth with frequent and strong strain. With these implementations, further, the form-closure snap-in-locking between locking and counterlocking element potentially occurs only after a certain displacement path. This occurs if during the closure of the clamping device, the teeth do not mesh with one another but come to lie one on the other. If this displacement path is to be kept short, the tooth must also be kept small which increases the loading of the tooth material.